|The MGA With An Attitude
ALUMINUM RADIATORS, The Basics -- CO-110
It is common for MGA owners to think they may have an overheating problem. Much of the time it is only a matter of personal perception and not actual overheating. While the thoughts are flying around some discussion often arises about possibly installing an aluminum radiator to reduce running temperature. Before you lay out big money for a custom hand built aluminum radiator, consider that it may not cool any better than the original copper radiator unless it is built in a significantly different form.
Vintage radiator cores are most often made with copper core and brass tanks. There is a good probability that car models designed prior to 1960 may originally have a cell core radiator, while later models may use tube cores. MGA originally had a cell core radiator. Cell cores have relatively large internal surface area, operate with some turbulence in the fluid, and transfer heat very efficiently from the fluid to the metal core matrix. Aside from being expensive to replace in modern times, there is the disadvantage of being difficult to clean out when it gets clogged inside. It can be chemically cleaned to some extent, but it cannot be manually routed out because of the convoluted fluid channels.
When rebuilding a radiator modern replacement cores are usually tube type cores, These have plain flattened tubes running through a matrix of thin air pass fins. The tube type cores are cheaper to manufacture and easy enough to manually route out if they get clogged (by removing one end tank). The fluid tubes have more laminar flow (less turbulenc), often less internal surface area, and may not transfer heat from fluid to metal matrix as efficiently as the cell core. Smooth laminar flow of fluid reduces heat transfer from fluid to metal as a thin film of slow moving fluid near the wall acts somewhat as an insulator. Therefore turbulence is a good thing for promoting heat transfer, and higher fluid velocity can also help for similar reason.
If the tube type core is slightly less efficient with heat transfer the coolant temperature may run a little higher in hot weather and harsh driving conditions. To retain equal cooling capacity the tube type core may need to be slightly larger. Given space constraints in original mounting configuration it is common to use more rows of tubes to increase internal surface area (which may still not equal the surface area of the original cell core).
It is also common to use more air fins closer together to increase external surface area of the core matrix. At some point this becomes counter-productive as closely spaced fins can begin to obstruct air flow. Modern cars most often have a shroud around the fan to improve air flow through the core at low travel speed. You might also install an aftermarket fan shroud on a vintage car if it does not have to conform to concours originality specifications.
Air flow is the holy grail of cooling, as a certain volume of air is needed to carry away a certain amount of heat with a certain temperature rise. The cooling system should work better at road speed with more air flow. If you have a situation where the coolant temperature increases dramatically with increasing road speed above 50 mph, then you probably have an air flow problem.
When thoughts turn to possibly installing an aluminum radiator, the first thing you should know is that pure copper conducts heat better than any alloy of aluminum, and almost all other metals are far worse (except pure silver). If you build an aluminum radiator in exactly the same configuration as the copper radiator, copper wins. This is why an aluminum radiator has to be different in physical configuration to improve heat transfer.
When I see an MGA with aluminum radiator my first impression is that it looks "clunky" and out of character for the vintage car. However, given that form follows function I may be willing to forgive the difference in appearance if it actually works better. Next thing I notice is that the aluminum radiator is often mated with an electric fan. The owner's comment is commonly something like, "It cools great. If the temperature starts to go a little high I switch on the electric fan and it cools right down". Oh? So what happens without the electric fan? And if the electric fan makes that much difference, why not just install the electric fan with the original copper (or replacement type copper) radiator? The third thing I notice is that the aluminum radiator is quite often larger than the original radiator, usually thicker in the core. Thicker core requires a wider bottom tank, which in turn may require some cut-back or roll-back of the sheet metal at rear of the body air pan.
Pure copper offers thermal conductivity up to 50% higher than aluminum, with comparable strength (78% higher in similar thickness). On these properties, some copper alloys overlap with the aluminum alloys. Standard copper alloys (e.g. brass) have similar strength but their thermal conductivities are typically lower than 1000 or 3000 series aluminum alloys (due to the high Zn content of brass). All other metals (except silver) have much lower thermal conductivity. As such, near pure copper is used for the radiator core while brass is commonly used for the tanks. Copper cores and brass tanks are as good as anything for cooling, but heavier than aluminum in a similar gauge. Aluminum can win on lower weight and cost of raw material, but custom hand fabrication can be a killer on cost.
|Substance ||k ||Temp|
|Silver ||242 ||70-600|
|Copper ||232 ||70-700|
|Gold ||196 ||60-212|
|Aluminum ||130 ||70-700|
|Brass (70%Cu/30%Zn) || 84.6 ||360-810|
|Zinc || 65 ||60-212|
|Steel (1%C) || 26.2 ||70-700|
|Lead || 20.3 ||32-500|
For the die hard technical heads, here is thermal conductivity for selected metals.
Thermal conductivity of the metal is not everything of course, especially since the metal is quite thin. Adequate fluid flow is important (but not usually a problem). Mass of air flow is very important and may sometimes be a problem. The point to all this is that an aluminum radiator will not cool better than a copper one when built in the same configuration.
If you still think you want an aluminum radiator for your MGA, then check CO-302 for commercially available units.